Method for the two-stage preparation of aqueous autocrosslinking copolymer dispersions and their use for coating materials

ABSTRACT

The invention concerns a two-stage method for the preparation of aqueous, self-crosslinking copolymer dispersions made from acrylate copolymers having acetoacetyl and carboxylic groups. The copolymers are neutralized with polyamines which act as crosslinking agents. These copolymers are useful in paints as binders that crosslink at room temperature or at elevated temperatures.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a two-stage method of preparing aqueous,autocrosslinking copolymer dispersions based on acrylate copolymerswhich have acetoacetyl groups and carboxyl groups and which areneutralized with polyamines which act as a crosslinking component, andto their use as binders for storage-stable one-component coatingmaterials and, in combination with low molecular mass polyisocyanates,as binders for two-component coating materials which crosslink at roomtemperature or at elevated temperature.

2. Description of Related Art

EP 0555774 A1 discloses a one-stage method of preparing such copolymerdispersions. The products, however, have a disadvantage. Firstly, a highproportion of acetoacetyl groups is required in order to achieve asufficient crosslinking density of the coating films; secondly, thishigh proportion of appropriate monomers brings about the formation,during the copolymerization, of bits and coagulum which can be removedagain only at great length and using complex apparatus.

SUMMARY OF THE INVENTION

It has surprisingly now been found that films of aqueous copolymerdispersions with small proportions of acetoacetyl groups also have ahigh crosslinking density if the emulsion copolymerization takes placeby a two-stage method in which monomers having in each case acetoacetylor carboxyl groups are employed only in the first stage.

The invention relates accordingly to a method of preparing aqueous,autocrosslinking copolymer dispersions whose monomer composition is

(Aa) from 3 to 35% by weight, preferably from 8 to 15% by weight, of(meth)acrylate monomers containing acetoacetyl groups,

A(b) from 1 to 20% by weight, preferably from 3 to 16% by weight, ofα,β-ethylenically unsaturated carboxylic acids, preferably (meth)acrylicacid,

A(c) from 11 to 96% by weight, preferably from 30 to 70% by weight, of(meth)acrylic alkyl esters and, if desired, diesters of maleic orfumaric acid, and

A(d) from 0 to 40% by weight, preferably from 0 to 25% by weight, ofother free-radically polymerizable monomers, such as vinyl aromaticcompounds, vinyl esters, hydroxyalkyl (meth)acrylates and(meth)acrylamide,

the sum of the percentages of components (Aa) to (Ad) necessarily being100, and the dispersions being neutralized with polyamines which act asa crosslinking component, which method is characterized in that

A) a two-stage free-radical emulsion polymerization is carried out, withthe proviso that in the first stage from 60 to 90% by weight of amixture of the monomers (Aa) to (Ad) and in the second stage from 10 to40% by weight of a mixture of the monomers (Ac) and (Ad) arecopolymerized, the sum of the percentages again necessarily being 100and the condition holding that the acrylate copolymers (A) containacetoacetyl groups in an amount of from 0.2 to 1.7 mol/kg, preferablyfrom 0.4 to 0.8 mol/kg, and carboxyl groups in an amount of from 0.15 to1.6 mol/kg, preferably from 0.4 to 0.75 mol/kg, and that the carboxylgroups are present in an amount of from 50 to 95 mol-%, preferably from80 to 90 mol-%, relative to the acetoacetyl groups,

and subsequently

B) the carboxyl groups of the copolymer dispersions (A) are reacted withpolyamines which contain at least two primary amino groups in themolecule, in a proportion of from 50 to 100 mol-%, preferably from 90 to100 mol-%, relative to the total primary amino groups, with salts beingformed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention additionally relates to the copolymer dispersions preparedin accordance with the invention and to their use as binders forstorage-stable one-component coating materials and, in combination withlow molecular mass polyisocyanates, as binders for two-component coatingmaterials which crosslink at room temperature or at elevatedtemperature.

The primary polyamines serve as neutralizing agents for stabilizing theaqueous copolymer dispersions and, finally, as a crosslinking componentduring film formation.

In accordance with the invention the copolymer dispersions are preparedby the method of a two-stage free-radical emulsion copolymerization in aknown manner. In this method the monomer components Aa) to Ad) definedin the main claim are employed in the stated proportions.

As monomer component (Aa) use is made of "N-diacetone(meth)acrylamide"(meth)acrylate monomers containing acetoacetyl groups, such as(meth)acrylic acetoacetoxyalkyl esters, preferably the ethyl ester.

As monomer component (Ad) examples of vinylaromatic compounds arestyrene and p-methylstyrene and an example of vinyl esters is vinylacetate.

The condition holds that the acrylate copolymers (A) contain acetoacetylgroups in an amount of from 0.2 to 1.7 mol/kg, preferably from 0.4 to0.8 mol/kg, and carboxyl groups in an amount of from 0.15 to 1.6 mol/kg,preferably from 0.4 to 0.75 mol/kg, and that the carboxyl groups arepresent in an amount of from 50 to 95 mol-%, preferably from 80 to 90mol-%, relative to the acetoacetyl groups.

Subsequently, the carboxyl groups of the copolymer dispersions (A) evenreacted with polyamines which have at least two primary amino groups inthe molecule, in a proportion of from 50 to 100 mol-%, preferably from90 to 100 mol-%, relative to the total primary amino groups, with saltsbeing formed.

Examples of polyamines are alkylenediamines, such as ethylenediamine andits homologs and isomers, and also diprimary polyalkylenepolyamines,such as diethylenetriamine, and other polyamines, such astrimethylolpropanehexaethoxytriamine or diprimary polyethoxydiamines.

The copolymer dispersions prepared in accordance with the invention havean excellent storage stability and give films having good resistanceproperties. They can be employed as binders for industrial coatings andprimers. In addition, they can be used to formulate clearcoats which areused for coating wood, plastic, leather or paper.

The copolymer dispersions are crosslinked by reacting the primary aminogroups of the polyamines with the keto groups of the acetoacetyl groupsof the copolymer dispersions (A) even at room temperature following theevaporation of a substantial proportion of the water.

With the proviso that hydroxyalkyl (meth)acrylates are among thosemonomers used as component (Ad), the copolymer dispersions can also becombined advantageously with low molecular mass polyisocyanates.

Polyisocyanates employed are customary commercial oligomers, for exampleisocyanurates, biuret types or allophanate types of aliphaticdiisocyanates, such as hexamethylene diisocyanate, isophoronediisocyanate or dicyclohexylmethane diisocyanate, in abinder/polyisocyanate ratio of from 90:10 to 60:40 (based on solids).

Two-component coating materials of this kind have relatively long potlives and, in comparison with one-component coating materials, in theform of coating films after a drying period of 4 weeks they possess notonly the expected higher crosslinking density but also a markedlyreduced tendency to bring about yellow discoloration of light-coloredwoods.

The formulation of water-thinnable coating materials using the bindersprepared in accordance with the invention, and the application of suchcoating materials, are known to the skilled worker.

The examples which follow illustrate the invention without restrictingit in its scope. All data in parts or percentages relate, unlessspecified otherwise, to units of weight.

1. EXAMPLES 1 TO 7 AND COMPARISON EXAMPLE V1 Example 1

In a reactor suitable for emulsion copolymerization, with refluxcondenser, thermometer and two feed vessels, a mixture of 360 parts ofdemineralized water, 24 parts of Triton X 200 (sodium alkylarylpolyethersulfonate, manufacturer: Rohm & Haas, USA) and 5.4 parts ofTriton X 165 (octylphenol ethoxylate, manufacturer: Rohm & Haas, USA) ishomogenized with stirring.

The feed vessel I is charged with a homogeneous emulsion consisting of1150 parts of demineralized water, 24 parts of Triton X 200, 10 parts ofTriton X 165, 3.2 parts of ammonium peroxodisulfate, 165 parts of butylmethacrylate, 280 parts of butyl acrylate, 275 parts of styrene, 140parts of acetoacetoxyethyl methacrylate and 40 parts of methacrylicacid. 5% of this preemulsion is run into the reactor. The contents ofthe reactor are heated to 85° C. with stirring and held at thistemperature for 10 minutes. The remaining contents of feed vessel I arethen metered into the reactor at a uniform rate over the course of 120minutes at 85° C.

Subsequently, a homogeneous emulsion of 100 parts of demineralizedwater, 3.1 parts of Triton X 200, 2.4 parts of Triton X 165, 30 parts ofbutyl acrylate, 70 parts of styrene and 0.8 parts of ammoniumperoxodisulfate is metered in from feed vessel II over the course of 30minutes at 85° C. After the end of the feed, the contents of the reactorare heated to 88° C. and held at this temperature for 120 minutes.Finally, they are cooled to 25° C., and 115 parts of a 20% strengthaqueous diethylenetriamine solution are added with stirring over thecourse of one hour. A 38.8% opalescent dispersion is obtained having amean particle size of 90 nanometres. The pH is 7.9.

Example 2 to 7 are prepared in analogy to Example 1. The compositions ofthe initial reactor charges and of the feeds, and altered polymerizationparameters, are given in Table 1, in which the following abbreviationsare used:

AAEMA acetoacetoxyethyl methacrylate

APS ammonium peroxodisulfate

AA acrylic acid

BA butyl acrylate

BMA butyl methacrylate

BV Hostapal BV conc. (Hoechst AG, DE)

DAMA diacetonemethacrylamide

DBF dibutyl fumarate

DETA diethylenetriamine

DW demineralized water

EHA 2-ethylhexyl acrylate

HBA 4-hydroxybutyl acrylate

HDA 1,6-hexamethylenediamine

HEMA 2-hydroxyethyl methacrylate

MA methacrylic acid

PMST p-methylstyrene

ST styrene

X 165 (Triton X 165) Rohm & Haas, USA)

X 200 (Triton X 200) Rohm & Haas, USA)

X 305 (Triton X 305) Rohm & Haas, USA)

(alkylaryl polyether alcohol)

Comparison Example V1

One-stage copolymer dispersion with high acetoacetoxy functionality(corresponding to Example 7 of EP 0555774 A1) In a reactor suitable foremulsion polymerization, 40 parts of DW and 27 parts of a liquorcontaining 80 parts of DW, 100 parts of a mixture of 45 parts of AAEMA,10.9 parts of AA, 28.1 parts of BA and 16 parts of BMA, 0.5 part ofTriton X 305, 1 part of dodecylsulfonate, 0.2 part of tert-dodecylmercaptan and 1 part of APS are heated to 85° C. The remaining 155.7parts of the liquor are added uniformly over the course of 2 hours froma feed vessel which is provided with a stirrer. The theoretical solidscontent of 45% is reached after a subsequent reaction time of 2 hours.The batch is cooled to 25° C. and neutralized with 31.2 parts of a 20%strength aqueous solution of DETA. The copolymer dispersion prepared inone stage contains fractions of bits and coagulum which require removalby filtration.

The characteristic data for the copolymer dispersions prepared inaccordance with Examples 1 to 7 and Comparison Example V1 are summarizedin Table 2.

                                      TABLE 1    __________________________________________________________________________                     Example                     1        2        3       4    __________________________________________________________________________    Initial reactor charge                     360 DW   420 DW   325 DW  325 DW                     24  X 200                              25  X 200                                       25  X 200                                               10  BV                     5.4 X 165                              7   X 165                                       7   X 165                                               7   X 165    Feed stream I    1150                         DW   1210                                  DW   1100                                           DW  1000                                                   DW                     24  X 200                              25  X 200                                       25  X 200                                               10  BV                     10  X 165                              5.6 X 165                                       5.6 X 165                                               5.6 X 165                     3.2 APS  5   APS  5   APS 5   APS                     165 BMA  195 MMA  185 EHA 250 ST                     280 BA   200 BA   420 BMA 285 BA                     275 ST   320 AAEMA                                       100 BA  120 AAEMA                     140 AAEMA                              85  AA   70  DAMA                                               45  MA                     40  MA            25  AA    % Feed stream I in initial reactor charge                      5       7.5      7.5     10    Feed time I (min)                     120      100      100     90    Feed stream II   100 DW   200 DW   200 DW  250 DW                     3.1 X 200                              6   X 200                                       6   X 200                                               5   BV                     2.4 X 165                              1.4 X 165                                       1.4 X 165                                               2   X 165                     0.8 APS  0.8 APS  0.8 APS 1   APS                     30  BA   150 BMA  150 ST  100 pMST                     70  ST   50  BA   50  EHA 150 BA                                               50  BMA    Feed time II (min)                      30      45       45      60    Neutralizing agent*                     23  DETA 43  HDA  17.5                                           DETA                                               29  HDA    __________________________________________________________________________                              Example                              5        6       7    __________________________________________________________________________             Initial reactor charge                              280 DW   325 DW  325 DW                              10  BV   25  X 200                                               10  BV                              7   X 305                                       7   X 165                                               7   X 165             Feed stream I    1100                                  DW   1100                                           DW  1000                                                   DW                              8   BV   25  X 200                                               10  BV                              5   X 305                                       5.6 X 165                                               5.6 X 165                              5   APS  5   APS 5   APS                              150 MMA  135 EHA 200 ST                              205 DBF  380 BMA 335 BA                              180 AAEMA                                       50  BA  120 AAEMA                              65  MA   100 DAMA                                               50  HEMA                                       100 HBA 45  MA                                       35  AA             % Feed stream I in initial reactor charge                              10       7.5     10             Feed time I (min)                              90       100     90             Feed stream II   300 DW   200 DW  250 DW                              7   BV   6   X 200                                               5   BV                              3   X 305                                       1.4 X 165                                               2   X 165                              1.2 APS  0.8 APS 1   APS                              200 ST   150 ST  100 pMST                              100 BA   50  EHA 100 BA                              100 BMA          50  BMA             Feed time II (min)                              60       45      60             Neutralizing Agent*                              34  DETA 25  DETA                                               29  HDA    __________________________________________________________________________     *as a 20% strength aqueous solution

                  TABLE 2    ______________________________________    Example       1        2       3      4    ______________________________________    Characteristic data    Solids content  %!                  38.8     35.8    39     38.6    pH            7.9      7.8     8      7.9    Mean particle size  nm!                  90       95      95     105    mol/kg AAc.sup.(1)                  0.65     1.5     0.38   0.56    mol/kg C.sup.(2)                  0.47     1.18    0.35   0.52    mol % C.sup.(3)                  72       79      92     93    mol % A.sup.(4)                  95       94      97     96    ______________________________________    Example       5        6       7      V1    ______________________________________    Characteristic data    Solids content  %!                  37.1     38.6    38.6   41.2    pH            7.6      8       7.9    8.2    Mean particle size  nm!                  100      90      105    180    mol/kg AAc.sup.(1)                  0.84     0.54    0.56   2.1    mol/kg C.sup.(2)                  0.76     0.49    0.52   1.51    mol % C.sup.(3)                  90       91      93     87    mol % A.sup.(4)                  87       90      96     80    ______________________________________     .sup.(1) Acetoacetyl groups     .sup.(2) Carboxyl groups     .sup.(3) mol % of carboxyl groups relative to AAc     .sup.(4) mol % of prim. amino groups relative to C

2. COATINGS PERFORMANCE TESTING OF THE COPOLYMER DISPERSIONS PREPARED INACCORDANCE WITH EXAMPLES 1 TO 5 AND PREPARED IN ACCORDANCE WITHCOMPARISON EXAMPLE V1 IN CLEARCOATS

The clearcloats 1 to 5 and V1 were prepared from 100 parts of binder (assolids), 0.8 part of a customary commercial antifoam, 0.2 part of acustomary commercial leveling agent, an optional rheology additive (e.g.PU thickener) and deionized water, and these clearcoats were subjectedto the following coatings performance tests whose results are summarizedin Table 3:

Freedom from tack: drying recorder, glass strips, 150 μm wet filmthickness, at 20° C. (stated in minutes)

Sandability: veneered wood, 150 μm wet film thickness; the parametertested is the clogging of sandpaper (grade 320) after 10 strokesfollowing a drying time of 60 minutes at room temperature (0=noclogging, MIN=minimal clogging.

KONIG pendulum hardness (DIN 53157): glass plates, 120 μm wet filmthickness, drying time of 24 hours at 20° C.

Resistance to acetone, ethanol and water: glass plates, 120 μm wet filmthickness, drying time of 24 hours at 20° C. A cotton wool padimpregnated with the solvent is placed on the film and covered with aglass beaker. The time is measured until the film softens.

                  TABLE 3    ______________________________________    Clearcoat   1      2       3    4     5    V1    ______________________________________    Freedom from tack in                20     15      20   15    20   15    minutes    Sandability 0      0       MIN  0     0    MIN    Pendulum hardness in                65     80      90   65    60   45    seconds    Acetone resistance in                >60    >60     >60  >60   >60  >60    seconds    Ethanol resistance in                >2     >2      >2   >2    >2   <0.25    seconds    Water resistance in                >24    >24     >24  >24   >24  <1    seconds    ______________________________________

3. COATINGS PERFORMANCE TESTING OF THE COPOLYMER DISPERSIONS PREPARED INACCORDANCE WITH EXAMPLES 6 AND 7 IN CLEARCOATS AND IN TWO-COMPONENTCOATING MATERIALS

Clearcoats 6 and 7 were prepared in analogy to clearcoats 1 to 5, butadditionally received per 100 parts in each case 10 or 20 parts ofBayhydur® LS 2032 (polyisocyanate based on hexamethylene diisocyanatewith a free isocyanate group content of about 17% and a solids contentof 100%, manufacturer: BAYER AG).

Two-component coating materials (6a and 7a) Binder:polyisocyanate=79.5:20.5 (based on solids) Solids content of the coatingmaterials: 44.5%

Two-component coating materials (6b and 7b) Binder: polyisocyanate=66:34(based on solids) Solids content of the coating materials: 49.2%

The clearcoats and two-component coating materials were subjected to thecoatings tests already mentioned and those indicated below, the resultsof which are summarized in Table 4:

Pot life: The two-component coating material is stirred once an hour.This operation is repeated until gelling begins.

Yellow discoloration: 200 μm wet film thickness on maple (veneered).Assessment is made after storage for 4 weeks at room temperature (1=nomeasurable discoloration, 5=very severe discoloration)

                  TABLE 4    ______________________________________    Clearcoat      6                  7    Two-component coating    material              6a     6b        7a   7b    ______________________________________    Freedom from tack in minutes                   20     25     50   20   25   40    Sandability    0      0      MIN  0    0    MIN    Pendulum hardness in seconds                   75     70     50   70   65   45    Acetone resistance in seconds                   >60    80     80   >60  70   90    Ethanol resistance in seconds                   >2     >5     >8   >2   >6   >10    Water resistance in seconds                   >24    >36    >48  >24  >36  >48    Potlife in hours                   --     >48    20   --   >48  25    Yellow discoloration                   4      2      1-2  4    2    1-2    ______________________________________

In addition to Table 4, the coating films of the two-component coatingmaterials 6a, 6b and 7a, 7b exhibit, in comparison with the clearcoats 6and 7, after a drying time of 4 weeks at room temperature, as expected,markedly better results in their resistance to acetone, ethanol andwater.

What is claimed is:
 1. A method for preparing an aqueous,autocrosslinking copolymer dispersion comprising:(A) polymerizingmonomers in a two-stage free-radical emulsion polymerization to preparea copolymer dispersion (A) with the proviso that, in the first stage,from 60 to 90% by weight of the dispersion including a mixture ofmonomers (Aa) to (Ad) are copolymerized, and in the second stage, from10 to 40% by weight of the dispersion including a mixture of themonomers (Ac) and (Ad) are copolymerized, where the sum of thepercentages is 100 when the first and second stage are added, and wherethe acrylate copolymers so produced contain acetoacetyl groups in anamount of from 0.2 to 1.7 mol/kg, carboxyl groups in an amount of from0.15 to 1.6 mol/kg, the carboxyl groups being present in an amount offrom 50 to 95 mol % relative to the acetoacetyl groups, the monomers(Aa), (Ab), (Ac) and (Ad) being defined as follows with the percentagesbeing the amount in the dispersion (A); (Aa) from 3 to 35% by weight ofone or more (meth)acrylate monomers containing acetoacetyl groups "orN-diacetone(meth)acrylamide" (Ab) from 1 to 20% by weight of α,β-ethylenically unsaturated carboxylic acids; (Ac) from 11 to 96% byweight of one or more (meth)acrylic alkyl esters or diesters of maleicor fumaric acid; and (Ad) from 0 to 40% by weight of otherfree-radically polymerizable monomers selected from the group consistingof vinylaromatic compounds, vinyl esters, hydroxyalkyl (meth)acrylatesand (meth)acrylamide,where the sum of the percentages of components (Aa)to (Ad) is 100; and (B) reacting carboxyl groups of the copolymerdispersion (A) with at least one polyamine that contains at least twoprimary amino groups in the molecule, in a proportion of from 50 to 100mol %, relative to the total primary amino groups.
 2. The method asclaimed in claim 1, wherein component (Ac) contains a diester of maleicor fumaric acid.
 3. The method as claimed in claim 1, wherein component(Aa) is selected from the group consisting ofN-diacetone(meth)acrylamide and (meth)acrylic acetodacetoxyalkyl esters.4. The method as claimed in claim 3, wherein component (Aa) is(meth)acrylic acetoacetoxyethyl ester.
 5. The method as claimed in claim1, wherein the vinyl aromatic compounds of component (Ad) are used andare selected from the group consisting of styrene and p-methylstyrene.6. The method as claimed in claim 1, wherein the vinyl ester ofcomponent (Ad) is used and is vinyl acetate.
 7. The method as claimed inclaim 1, wherein the polyamine of step (B) is selected from the groupconsisting of ethylenediamine, diethylenetriamine, trimethylolpropanehexaethoxytriamine, and diprimary polyethoxydiamines.
 8. An aqueous,auto-cross-linking copolymer dispersion prepared in accordance with themethod of claim
 1. 9. The dispersion as claimed in claim 8, whereincomponent (Ac) contains a diester of maleic or fumaric acid.
 10. Thedispersion as claimed in claim 8, wherein component (Aa) is selectedfrom the group consisting of N-diacetone(meth)acrylamide and(meth)acrylic acetoacetoxyalkyl esters.
 11. The dispersion as claimed inclaim 10, wherein the component (Aa) is (meth)actylic acetoacetoxyethylester.
 12. The dispersion as claimed in claim 8, wherein the vinylaromatic compounds of component (Ad) are used and are selected from thegroup consisting of styrene and p-methylstyrene.
 13. The dispersion asclaimed in claim 8, wherein the vinyl ester of component (Ad) is usedand is vinyl acetate.